Disclosed herein are ink carriers, phase change inks and methods for making same. More specifically, disclosed herein are ink carriers and phase change inks including at least one of surface modified silica nanoparticles and surface modified metal oxide nanoparticles which can be used in direct and indirect printing processes. In embodiments, the phase change inks are of the low energy type. In various embodiments, the ink carriers comprise a dispersion of at least one of surface modified silica nanoparticles and surface modified metal oxide nanoparticles.
Another embodiment is directed to a method which comprises (a) incorporating into an ink jet printing apparatus the above-described phase change ink composition; (b) melting the ink; (c) causing droplets of the melted ink to be ejected in an imagewise pattern onto the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, where the droplets quickly solidify to form a predetermined pattern of solidified ink drops.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes.
The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labeling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 3,653,932, U.S. Pat. No. 4,390,369, U.S. Pat. No. 4,484,948, U.S. Pat. No. 4,684,956, U.S. Pat. No. 4,851,045, U.S. Pat. No. 4,889,560, U.S. Pat. No. 5,006,170, U.S. Pat. No. 5,151,120, U.S. Pat. No. 5,372,852, U.S. Pat. No. 5,496,879, European Patent Publication 0187352, European Patent Publication 0206286, German Patent Publication DE 4205636AL, German Patent Publication DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference, ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are at least three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In a typical design of a piezoelectric ink jet device utilizing phase change inks printing directly on a substrate or on an intermediate transfer member, such as the one described in U.S. Pat. No. 5,372,852, incorporated herein by reference, the image is applied by jetting appropriately colored inks during four to eighteen rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Thermal ink jet processes are well known and are described, for example, in U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224 and 4,532,530, the disclosures of each of which are hereby incorporated herein.
Ink jet printing processes may employ inks that are solid at room temperature and liquid at elevated temperatures. Such inks may be referred to as hot melt inks or phase change inks. For example, U.S. Pat. No. 4,490,731, which is hereby incorporated by reference herein, discloses an apparatus for dispensing solid ink for printing on a substrate such as paper. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by the heater in the printing apparatus and utilized (i.e., jetted) as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the colorant to substantially remain on the surface of the substrate instead of being carried into the substrate (for example, paper) by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a phase change ink in ink jet printing are thus elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
Examples of the phase change inks herein are inks that include an ink vehicle that is solid at temperatures of about 23° C. to about 27° C., for example room temperature, and specifically are solid at temperatures below about 60° C. However, the inks change phase upon heating, and are in a molten state at jetting temperatures. Thus, the inks have a viscosity of from about 1 to about 20 centipoise (cp), for example from about 5 to about 15 cp or from about 8 to about 12 cp, at an elevated temperature suitable for ink jet printing, for example temperatures of from about 60° C. to about 150° C.
In this regard, the inks herein may be either low energy inks or high energy inks. Low energy inks are solid at a temperature below about 40° C. and have a viscosity of from about 1 to about 20 centipoise such as from about 5 to about 15 centipoise, for example from about 8 to about 12 cp, at a jetting temperature of from about 60° C. to about 100° C. such as about 80° C. to about 100° C., for example from about 90° C. to about 100° C. High energy inks are solid at a temperature below 40° C. and have a viscosity of from about 5 to about 15 centipoise at a jetting temperature of from about 100° C. to about 180° C., for example from 120° C. to about 160° C. or from about 125° C. to about 150° C.
See Nolte, et al., “Additives Containing Nano Metal Oxides for Enhanced Scratch Resistance in Coating Formulations,” NSTI-Nanotech 2007, Vol. 4, pp. 199-201, which is hereby incorporated by reference herein. See also Etienne, et al., “Effects of Incorporation of Modified Silica Nanoparticles on the Mechanical and Thermal Properties of PMMA,” Journal of Thermal Analysis and Calorimetry, 2007, 87, pp. 101-104, which is hereby incorporated by reference herein. See also, J. Hajas, et al., “Surface Modified Silica Nanoparticles to Improve Scratch Resistance of Solvent Borne Coatings,” European Coatings, 2006, 82(46), pp. 19-23, which is hereby incorporated by reference herein. Also see R. P. Bagwe, et al., “Surface Modification of Silica Nanoparticles to Reduce Aggregation and Nonspecific Bonding,” Langmuir, Vol. 22, No. 9, 2006, page 4357-4362, which is hereby incorporated by reference herein.
While known compositions and processes are suitable for their intended purposes, the images currently produced by the phase change inks in many instances, exhibit poor scratch resistance and image permanence. A need remains for improved phase change inks, and more specifically, phase change inks which exhibit improved image quality and robustness, that is resistance to scratch, crease and abrasion with substantially no smear, and image permanence. Additionally, a need remains for phase change inks that print successfully on paper and transparency stock. Furthermore, there is a need for phase change inks that generate prints with good performance in automatic document feeders.
The appropriate components and process aspects of the each of the foregoing may be selected for the present disclosure in embodiments thereof.